NATURAL HISTORY. 
Sea Thread. Of frequent occurrence on old 
shells, &c. 
TUBULARIA. Inoprvisa. Ellis’s Corall. p, 31. 
n. 2, t. 16. Frequent on shells from deep water. 
4. NUDA. 
Naked polypi, with tentaculi round the mouth, 
HYDRA. Vrrrprs.  Ellis’s Corall. t. 28. C, 
Frequent on aquatic plants in slow streams. 
The Individuals arranged under this last type oc- 
cupy the lowest situation in the scale of Animal ex- 
istance ;—The nervous system in all of them being 
very obscure and, in not a few of the species, only 
recognizable with considerable difficulty. Still 
many of them are of considerable importance as for- 
ming extensive reefs and Islands in the warmer re- 
gions of the globe, tho’ in this respect their opera- 
tions appear to be much less extensive than was at 
one time supposed ; and others from their elegant 
forms and curious modes of propagation, are very 
interesting subjects of investigation.—The greater 
part of them were mistaken by our earlier naturalists 
for plants, and it is to Ells that we are indebted 
for first clearly pointing out their animal nature, in 
his ‘‘Essay towardsa natural History of Corallines’’ 
London, 1755; this is the work we have chiefly 
referred to for this class, and we know of no su- 
perior one from which to obtain a clear idea of the 
